Sally A. Viken

Demonstration of four operating capabilities to enable a small aircraft transportation system

The small aircraft transportation system (SATS) project has been a five-year effort fostering research and development that could lead to the transformation of our countrys air transportation system. It has become evident that our commercial air transportation system is reaching its peak in terms of capacity, with numerous delays in the system and the demand keeps steadily increasing. The SATS vision is to increase mobility in our nations transportation system by expanding access to more than 3400 small community airports that are currently under-utilized. The SATS project has focused its efforts on four key operating capabilities that have addressed new emerging technologies and procedures to pave the way for a new way of air travel. The four key operating capabilities are: higher volume operations at nontowered/nonradar airports, en route procedures and systems for integrated fleet operations, lower landing minimums at minimally equipped landing facilities, and increased single pilot performance. These four capabilities are key to enabling low-cost, on-demand, point-to-point transportation of goods and passengers utilizing small aircraft operating from small airports. The focus of this paper is to discuss the technical and operational feasibility of the four operating capabilities and demonstrate how they can enable a small aircraft transportation system.

Computational Analysis of a Wing Designed for the X-57 Distributed Electric Propulsion Aircraft

A computational study of the wing for the distributed electric propulsion X-57 Maxwell airplane configuration at cruise and takeoff/landing conditions was completed. Two unstructured-mesh, Navier-Stokes computational fluid dynamics methods, FUN3D and USM3D, were used to predict the wing performance. The goal of the X-57 wing and distributed electric propulsion system design was to meet or exceed the required lift coefficient 3.95 for a stall speed of 58 knots, with a cruise speed of 150 knots at an altitude of 8,000 ft. The X-57 Maxwell airplane was designed with a small, high aspect ratio cruise wing that was designed for a high cruise lift coefficient (0.75) at angle of attack of 0°. The cruise propulsors at the wingtip rotate counter to the wingtip vortex and reduce induced drag by 7.5 percent at an angle of attack of 0.6°. The unblown maximum lift coefficient of the high-lift wing (with the 30° flap setting) is 2.439. The stall speed goal performance metric was confirmed with a blown wing computed effective lift coefficient of 4.202. The lift augmentation from the high-lift, distributed electric propulsion system is 1.7. The predicted cruise wing drag coefficient of 0.02191 is 0.00076 above the drag allotted for the wing in the original estimate. However, the predicted drag overage for the wing would only use 10.1 percent of the original estimated drag margin, which is 0.00749. Nomenclature CD drag coefficient Vt,ratio ratio of tip speed to freestream velocity CD,HLN drag coefficient, high-lift nacelles contribution W aircraft weight, lb CD,pylons drag coefficient, pylons contribution y axis along the wing span, in. CD,TN drag coefficient, wingtip nacelles contribution y + nondimensional first node height in boundary layer CD,wing Cf drag coefficient, wing contribution skin friction coefficient yCC + nondimensional first cell centroid height in boundary layer CL lift coefficient Symbols cl sectional lift coefficient  angle of attack, degrees CL,eff effective lift coefficient: CL+ CL,prop Δ delta CL,max maximum lift coefficient ρ density CL,prop lift coefficient from the contribution of propeller thrust in lift direction Acronyms BSL Menter k-ω basic turbulence model Cm pitching moment coefficient CFL pseudo time advancement Courant-Friedrichs-Lewy Cp pressure coefficient DEP distributed electric propulsion Cref reference chord, in. HLN high-lift nacelles, including pylons CT thrust coefficient HP horse power CQ torque coefficient KCAS knots calibrated airspeed D drag force KEAS knots equivalent airspeed d propeller diameter, ft. KTAS knots true airspeed h altitude, ft. LM Langtry-Menter transition model KT normalized thrust coefficient mph miles per hour KQ normalized torque coefficient QCR quadratic constitutive relation M Mach number RPM revolutions per minute P pressure, lbf/in SA Spalart-Almaras one equation turbulence model q dynamic pressure SARC SA rotation and curvature correction Re S Reynolds number based on Cref wing reference area, ft SCEPTOR Scalable Convergent Electric Propulsion Technology and Operations Research T temperature, °F SST Menter’s Shear Stress Transport model V freestream velocity, ft/sec TN wingtip nacelles * Aerospace Engineer, Configuration Aerodynamics Branch, Mail Stop 499, AIAA Senior Member. † Aerospace Engineer, Aeronautics Systems Analysis Branch, Mail Stop 442, AIAA Senior Member. ‡ Aerospace Engineer, Configuration Aerodynamics Branch, Mail Stop 499, AIAA Associate Fellow. § Senior Researcher, GEOLAB, Mail Stop 128. ** Technical Group Lead, GEOLAB, Mail Stop 128. https://ntrs.nasa.gov/search.jsp?R=20170005883 2019-12-26T23:55:46+00:00Z

Design of the Cruise and Flap Airfoil for the X-57 Maxwell Distributed Electric Propulsion Aircraft

A computational and design study on an airfoil and high-lift flap for the X-57 Maxwell Distributed Electric Propulsion (DEP) testbed aircraft was conducted. The aircraft wing sizing study resulted in a wing area of 66.67 ft2 and aspect ratio of 15 with a design requirement of Vstall = 58 KEAS, at a gross weight of 3,000 lb. To meet this goal an aircraft CL,max of 4.0 was required. The design cruise condition is 150 KTAS at 8,000 ft. This resulted in airfoil requirements of cl ~ 0.90 for the cruise condition at Re = 2.35 x 106. A flapped airfoil with a cl,max of approximately 2.5 or greater, at Re = 1.0 x 106, was needed to have enough lift to meet the stall requirement with the DEP system. MSES computational analyses were conducted on the GAW-1, GAW-2, and the NACA 5415 airfoil sections, however they had limitations in either high drag or low cl,max on the cruise airfoil, which was the impetus for a new design. A design was conducted to develop a low drag airfoil for the X-57 cruise conditions with high cl,max. The final design was the GNEW5BP93B airfoil with a minimum drag coefficient of cd = 0.0053 at cl = 0.90 and achieved laminar flow back to 69% chord on the upper surface and 62% chord on the lower surface. With fully turbulent flow, the drag increases to cd = 0.0120. The predicted maximum lift with turbulent flow is a cl,max of 1.95 at  = 19°. The airfoil is characterized by relatively flat pressure gradient regions on both surfaces at  = 0°, and aft camber to get extra lift out of the lower surface concave region. A 25% chord slotted flap was designed and analyzed with MSES for a 30° flap deflection. Additional 30° and 40° flap deflection analyses for two flap positions were conducted with USM3D using several turbulence models, for two angles of attack, to assess near cl,max with varied flap position. The maximum cl varied between 2.41 and 3.35. An infinite-span powered high-lift study was conducted on a GAW-1 constant chord 40° flapped airfoil section with FUN3D to quantify the airfoil lift increment that can be expected from a DEP system. The 16.7 hp/propeller blown wing increases the maximum CL from 3.45 to CL = 6.43, which is an effective q ratio of 1.86. This indicates that if the unblown high-lift flapped airfoil of the X-57 airplane achieves a cl,max of 2.78, then the high-lift augmentation blowing could yield a sectional lift coefficient of approximately 4.95 at cl,max. Finally, a computational study was conducted with FUN3D on an infinite-span constant chord GAW-1 cruise airfoil to determine the impact of high-lift propeller diameter to wing chord ratio on the lift increment of the DEP system. A constant diameter propeller and nacelle size were used in the study. Three computational grids were made with airfoil chords of 0.5*chord, 1.0*chord, and 2.0*chord. Results of the propeller diameter to wing chord ratio study indicated that the blown to unblown CL ratio increased as the chord was decreased. However, because of the increase in relative size of the high-lift nacelle to the wing, which impacted wing lift performance, the study indicated that a propeller diameter to wing chord ratio of 1.0 gives the overall best maximum lift on the wing with the DEP system.

Overview of the Small Aircraft Transportation System Project Four Enabling Operating Capabilities

It has become evident that our commercial air transportation system is reaching its peak in terms of capacity, with numerous delays in the system and the demand still steadily increasing. NASA, FAA, and the National Consortium for Aviation Mobility (NCAM) have partnered to aid in increasing the mobility throughout the United States through the Small Aircraft Transportation System (SATS) project. The SATS project has been a five-year effort to provide the technical and economic basis for further national investment and policy decisions to support a small aircraft transportation system. The SATS vision is to enable people and goods to have the convenience of on-demand point-to-point travel, anywhere, anytime for both personal and business travel. This vision can be obtained by expanding near all-weather access to more than 3,400 small community airports that are currently under-utilized throughout the United States. SATS has focused its efforts on four key operating capabilities that have addressed new emerging technologies, procedures, and concepts to pave the way for small aircraft to operate in nearly all weather conditions at virtually any runway in the United States. These four key operating capabilities are: Higher Volume Operations at Non-Towered/Non-Radar Airports, En Route Procedures and Systems for Integrated Fleet Operations, Lower Landing Minimums at Minimally Equipped Landing Facilities, and Increased Single Pilot Performance. The SATS project culminated with the 2005 SATS Public Demonstration in Danville, Virginia on June 5th-7th, by showcasing the accomplishments achieved throughout the project and demonstrating that a small aircraft transportation system could be viable. The technologies, procedures, and concepts were successfully demonstrated to show that they were safe, effective, and affordable for small aircraft in near all weather conditions. The focus of this paper is to provide an overview of the technical and operational feasibility of the four operating capabilities, and explain how they can enable a small aircraft transportation system.